This invention relates to a color photographic material and more particularly to a direct reversal color photographic material useful in color diffusion transfer processes.
Photosensitive materials wherein colored dye image-providing compounds having a ready-made dye structure (i.e., pre-existing chromophiric group) in the molecule are combined with silver halide photosensitive emulsion are known. To avoid speed losses resulting from light absorption, soft gradation and other disadvantages, the following three techniques are commonly used (either solely or jointly): (1) silver halide emulsions and dye image-forming compounds are incorporated in separate layers, in such a manner that three pairs of emulsion layers selectively sensitive to light in different spectral regions and layers containing dye image-providing compounds that selectively absorb light in these different spectral regions are located adjacent thereto, with each emulsion layer positioned closer to the exposing side (that is, the side from which imagewise light exposure is made) of the photosensitive material; (2) intermediate layers are disposed between the three combinations of emulsion layer/layer containing dye image-providing compound; and (3) using an internal latent image-forming silver halide emulsion of direct reversal type and dye releasing redox compound as the dye image-providing compound, respectively. For further details, see The Theory of the Photographic Process, T. H. James, Ed., 4th Ed., p. 370 (1977), Macmillan Publishing Co., Inc. Negative emulsions for releasing development inhibitors can be incorporated in the interlayers in a structure as described above, as is taught in German Pat. (DE-AS) No. 2,258,967 (Example 10) and German Pat. (DE-AS) No. 2,516,408 (Example 1).
FIG. 1 shows a color photographic material comprising a support (not shown) having disposed thereon, in the order going from the exposing side (i.e., in sequence, although other layers may also be present):
(1) a first emulsion layer (indicated by 1 in FIG. 1) that contains an internal latent image-forming silver halide reversal emulsion that is selectively sensitive to light in a first spectral region; PA0 (2) a first color material layer (indicated by 2 in FIG. 1) that contains a ballasted compound that provides, upon a redox reaction, a dye image that selectively absorbs light in the first spectral region (said compound being hereinafter referred to as a dye releasing redox compound (also known as a DRR compound)); PA0 (3) an intermediate layer (indicated by 3 in FIG. 1) that contains a ballasted reducing agent that captures an oxidized developing agent used as an electron transfer agent; PA0 (4) a second emulsion layer (indicated by 4 in FIG. 1) that contains an internal latent image-forming silver halide reversal emulsion that is selectively sensitive to light in a second spectral region; and PA0 (5) a second color material layer (indicated by 5 in FIG. 1) that contains a dye-releasing redox compound that selectively absorbs light in the second spectral region. PA0 (1) a first emulsion layer containing an internal latent image forming direct reversal silver halide emulsion which is selectively sensitive to light in a first spectral region; PA0 (2) a first color material layer containing a ballasted dye releasing redox compound that provides a dye image that selectively absorbs light in the first spectral region; PA0 (3) an intermediate layer that contains a ballasted reducing agent capable of capturing an oxidized developing agent (i.e., electron transfer agent); PA0 (4) a second emulsion layer containing an internal latent image forming direct reversal silver halide emulsion that is selectively sensitive to light in the second spectral region; and PA0 (5) a second color material layer that contains a ballasted dye releasing redox compound that provides a dye image that selectively absorb light in the second spectral region,
The side from which the imagewise light exposure is made is indicated in FIG. 1 by "Exp".
When such photographic material is processed with an aqueous alkaline solution containing a developing agent after imagewise exposure, the following phenomena take place to form an imagewise distribution of dye.
The developing agent coming within these photographic layers develop the first and second emulsion layers so as to provide direct reversal images. The oxidized developing agent migrates to the adjacent first and second color material layers to oxidize the dye releasing redox compounds in these layers. As a result of this cross-oxidation, the diffusable dyes are released and an imagewise distribution of the released diffusable dyes and the remaining dye-releasing redox compounds is formed. If the first color material layer was in direct contact with the second emulsion layer, at least part of the oxidized developing agent coming from the first emulsion layer would pass through the first color material layer and react with the second color material layer. Further, a considerably greater part of the oxidized developing agent coming from the second emulsion layer would react with the first color material layer to release the dye whose light absorption does not correctly correspond to the color sensitivity of the emulsion layer. To provide a correct correspondence between the color sensitive area of emulsion layers and the light-absorbing area of dye images, an intermediate layer containing a reducing agent that is highly reactive to the oxidized developing agent is disposed between the first color material layer and the second emulsion layer. This reducing agent is said to "capture" the oxidized developing agent. In most cases, the first spectral region and the second spectral region are selected from the wavelength regions of from about 400 to 500 nm, and from about 500 to about 600 nm (conventionally a third emulsion layer sensitive to a third spectral region of from about 600 to 700 nm is also employed), according to the principle of color reproduction by the subtractive color process. Therefore, typically suitable emulsion/dye releasing redox compound combinations are selected from the combination of a blue-sensitive emulsion and yellow dye-releasing redox compound, the combination of a green-sensitive emulsion and magenta dye-releasing redox compound, and the combination of a red-sensitive emulsion and cyan dye-releasing redox compound.
However, the color reproduction of a photosensitive material of the structure shown in FIG. 1 is by no means satisfactory even after a proper correspondence of cross-oxidation is assured between the color sensitive area of emulsion layers and the light-absorbing area of dye images. One defect is attributable to the fact that the degree of formation of a dye image from the combination of the first emulsion layer and the first color material layer depends not only on the amount of exposure in the first spectral region but also on the amount of exposure in the second spectral region, i.e., the degree of development of the second emulsion layer. Even if a uniform exposure is achieved in the first spectral region, a large amount of dye tends to be generated from the first color material layer if the second emulsion layer contains a large quantity of developed silver, and a small amount of dye tends to be generated from the first color material if the second emulsion layer contains a small quantity of developed silver. In other words, a large amount of dye is generated in shadow portions of the image, where both the first and second emulsion layers are developed, but at monochromatic portions where only the first emulsion layer is developed, a small amount of dye is generated to give light monochromatic reproduction with a low degree of saturation. In a 3-primary color subtractive color reproducing photographic system comprising three laminated emulsion units sensitive to three spectral regions as noted above, high optical density is obtained in a black portions of the image, where three colors overlap each other, but only low optical density is obtained in monochromatic (yellow or magenta) areas and dichromatic (blue, green, or red) areas, producing a color print which has no sharpness in color and hence requires improvement. Such a defect in color reproduction is referred to as the "negative interimage effect", wherein the development of smulsion layers having different color sensitivities produces mutually intensifying dye images.
Another defect of the photosensitive material of the structure shown in FIG. 1 is poor color reproduction due to reductive deterioration of photographically useful components that is caused by the strong reduction power that the reducing agent in the intermediate layer (interlayer) exhibits under alkaline conditions achieved by development. An example of such deterioration is an irreversible discoloration of an image dye due to reduction.